1. Field of the Invention
This invention relates to a waterproofing agent for cable, a waterproofing tape, waterproofing yarns, an absorbent composition, and a waterproofing agent containing the composition. More particularly, it relates to a waterproofing agent which prevents water, particularly a highly concentrated saline water such as seawater, from entering the sheath of a varying cable such as are embracing communication grade cables like optical cables and metallic cables and electric cables, migrating within the sheath, and deteriorating the cable itself or various devices connected thereto, a waterproofing tape, waterproofing yarns, a absorbent composition, and a waterproofing agent containing the composition.
2. Description of the Prior Art
When the sheath of a cable sustains an external injury and suffers infiltration of water, the water rapidly migrates within the sheath and deteriorates the optical fiber or electric line of the cable or various devices connected thereto. A method for solving this problem by filling the sheath interior with a waterproofing agent, a waterproofing tape, or waterproofing yarns invariably made of absorbent resin or with an absorbent has been proposed.
The absorbent resins which have been heretofore used for this purpose include cross-linked polysodium acrylate, neutralized starch-acrylic acid graft copolymer, saponified vinyl acetate-acrylic ester copolymers, and neutralized cross-linked isobutylene-maleic anhydride copolymer, for example.
Since the absorbent resins mentioned above, when used in their independent form, absorb water slowly, they are made to absorb water quickly by a method such as the addition of an inorganic powder (JP-A-56-133,028(1981)). This method faces as a problem the fact that the slippage between gel particles is impaired by the added inorganic powder (because of excessive increase in the gel viscosity) and, depending on the construction of the cable, the absorbent resin suffers an eventual decline of its waterproofing ability because the gel is not allowed to migrate to the path of infiltration of water.
Further, the absorbent resins mentioned above face as a problem thereof the fact that since they are deficient in ability to absorb saline water, these absorbent resins used in cables fail to prevent infiltration of water when the cables are buried under ground or under sea bottom.
The waterproofing tapes heretofore used have been produced by having such absorbent resins as cross-linked polysodium acrylate, neutralized starch-acrylic acid graft polymer, saponified vinyl acetate-acrylic ester copolymers, and neutralized cross-linked isobutylene-maleic anhydride copolymer deposited fast on non-woven fabrics (JP-A-64-76,609(1989) and JP-U-61-129,228(1986)). The waterproofing tapes mentioned above, however, are problematic in that because the waterproofing tapes absorb water at unduly low speeds and exhibit no sufficient ability to absorb saline water and because the absorbent resins used therein have no appropriate gel viscosity, the waterproofing tapes used in cables buried under ground or under sea bottom allow no sufficient prevention of infiltration of water.
It has been proposed to produce an absorbent tape of an excellent ability to cut off seawater by impregnating a substrate such as non-woven fabric with a water-soluble polymer like a sulfoalkyl(meth)acrylate or acrylamide and a cross-linking agent and subsequently cross-linking the polymer deposited in the substrate (JP-A-2-11,690(1990)). The waterproofing tape which has the substrate and the absorbent resin integrated fast as described above, however, faces as a problem the fact that it absorbs water at a low speed and, therefore, possesses only poor ability to cut off water.
The waterproofing yarns currently in popular use are produced by having such absorbent resins as cross-linked polysodium acrylate, neutralized starch-acrylic acid graft polymer, saponified vinyl acetate-acrylic ester copolymers, and neutralized cross-linked isobutylene-maleic anhydride copolymers deposited fast on non-woven fabrics (JP-A-62-259,305(1987) and JP-A-63-241,806(1988)). The waterproofing yarns mentioned above, however, face as a problem the fact that these waterproofing yarns, when used in cables buried under ground or under sea bottom, are incapable of fully preventing infiltration of water because the waterproofing yarns absorb water at a low speed and exhibit no sufficient ability to absorb saline water and because the absorbent resins used therein have no appropriate gel viscosity.
An object of this invention, therefore, is to provide a novel waterproofing agent for use in cables, a waterproofing tape, waterproofing yarns, an absorbent composition, and a waterproofing agent containing the absorbent composition.
Another object of this invention is to provide a cable grade waterproofing agent possessing an outstanding salt-resisting property such as to retain the speed of water absorption and the ability of water absorption thereof intact on exposure even to highly concentrated saline water entering the sheath of a cable and to manifest the waterproofing ability stably for a long time, a waterproofing tape, waterproofing yarns, an absorbent composition, and a waterproofing agent containing the absorbent composition.